Signal transmission control system



H, BEIZER 1,951,333

SIGNAL TRANSMISSION CONTROL SYSTEM- Filed June 27, 1952 2 sheets-sheet 1 b21/Pow .5E/2f@ wf/WOR y @mf/WM Arrow/fr n h m o 0m m 'l1 .V 9.

March 20, 1934.

March 20, 1934. H. BElzr-:R

SIGNAL TRANSMISSION CONTROL SYSTEM Filed June 27. 1932 2 Sheets-Sheet 2 fis-H Patented Mar, 2Q, i934 reim 2l- Claims.

This invention relates to signal transmission control apparatus.

An object oi my invention is to produce an arrangement whereby the range of intensities of t signal may be reduced from excessive values to smaller permissible values.

another obect of my invention is to enable a signal which has been reduced in. its intensity range to be brought back to any desired range of intensities.

A still further object is to produce the above changes in the range of intensities of a signal without the introduction of distortion.

The foregoing and other objects of my invention will be best understood from the following description ci exempliiications thereof, reference being had to the accompanying drawings, where- Fig. i is a diagrammatic representation of an li embodiment of my invention;

Fig. 2 shows certain specific arrangements of certain elements of Fig, l;

rig. 3 shows an alternative arrangement or" the amplifier' stage shown in Fig. 2;

g. fi shows anot er alternative arrangement of amplifier stage;

Fig; shows another embodiment of one of the ele nts of Fig. l; and

Figs. ii, S, 9, l0 and ll are possible characteristic curves of the various elements oi my system.

Practically every device which is utilized to transmit signals has a limited range of signal intensities which can transmit satisfactorily. Such a device may be, for example, a telephone line, a radio transmitter, or the like. When the signal to be transmitted, for example, consists of audio frequency currents corresponding to sounds, the above devices introduce distortions into the signal whenever these signals are above or below a certain range of intensities, which distortions are readily perceived by the listener at the receiving end of the system. If the intensity or amplitude of the signal wave rises above a certain value, distortion will be introduced by the iiattening out of the tops of the signal wave. Thus the signal intensity should not be allowed to rise above a predetermined upper value. In such syst ms there is always a certain amount so of electrical disturbances due to a large number of causes, which disturbances manifest themselves as noise or static. ln the case of telephone lines, signal currents flowing in each telecircuit induce small currents in neighboring circuits. "lhese induced currents constitute a disturbance which is commonly called crosstallr. lf the signal intensity is appreciably above the intensity level of these disturbances, they can be suppressed. if, however, the signal intensity falls to the order of or below the disturbance level, they cannot be suppressed or separated from the signal variations, and are heard at the receiving end of the system. Thus the signal intensity should not be allowed to all below a predetermined lower value. The above is true for signals other than those involved in the transmission oi sounds. Such signals may be, for example, those involved in the transmission of visual scenes, supersonic frequencies and the like. This problem is not limited to the particular devices mentioned above, but exists in various other systems. For example, in recording sounds on films or on grooved records, the upper level of signal intensity is limited by the width of sound track or sound groove, respectively. lThe lower level may be restricted by the grain of the recording material, by the noise disturbance level as mentioned above, and by various other factors.

in order to avoid the above difficulties, it is desirable to produce an arrangement which will compress the range of intensities or amplitudes of signal variations to the range which can be handled satisfactorily by the system involved. A signal so compressed of course will not correspond exactly to the original signal, and must be expanded to its original range of intensities in order that the received signal be a true representation of that transmitted. For example, in the case of the transmission of sound, the compressed signal if not expanded will not be normally loud at the upper signal intensities, and the listeners ear will introduce appreciable distortion due to the fact that it responds dierently at different levels of sound intensity. Also the unexpanded signal, in the case of music or speech, will not contain all of the expression which the performers originally gave to it. Thus the signal before it reaches the receiving apparatus should be eX- panded to its original range or" intensities. In some instances, however, it may be satisfactory or even desirable to have the received signal of a different range of intensities than that transmitted. For example, a signal may be transmitted over a telephone line and compressed to the range of intensities which can be satisfactorily handled by said line. It may be desired to send said signal from said line out over a radio transmitter which can handle a somewhat higher range of intensities. Even though the range which can be transmitted by the transmitter may be less than the range of the original signal, yet by expanding the signal as it comes from the telephone line to the range that the radio transmitter can satisfactorily handle, the resulting signal will be a closer approximation to the original signal than if it were not expanded at all. Ho-wever, in every case it is desirable that the system of compression and expansion of the signal be as free from the introduction of distortion as possible.

In accordance with my invention I accomplish the desired results set forth above by impressing the signal to be transmitted upon an amplifier whose gain is varied by the function of the intensity of the impressed signal. By intensity I mean, in the case of a simple sine wave signal, the maximum amplitude which a single cycle reaches, while in the case of a complex wave, the intensity is the summation of the intensities of the individual sine wave components of the signal. Instead of an amplifier, it is also possible to use a device which attenuates the signal passing through it. In such a device the attenuating power thereof is varied by a function of the intensity of the impressed signal. At the transmission end of the system I use a device arranged so that the signal intensities are compressed, while at the receiving end of the system I use a device arranged so that the signal is correspondingly expanded. The transmission and receiving ends of the system as herein stated are not necessarily the actual terminals of a complete and independent system. For example, in a transmission system there may be a certain portion which has a more limited amplitude transmission capacity than the rest of the system. In that case the transmission and receiving ends of the system may mean the ends of that certain portion of the entire transmission system having the limited transmission capacity.

If any function of the signal wave other than the intensity is used to control the gain of the amplifier or to regulate the attenuator, considerable distortion of the signal wave results, which inthe case of the transmission of sound can readily be heard by the listener. If, for example, the instantaneous amplitude of the signal wave is used as the regulating function, higher frequency distortions are introduced into the signal. Many transmitting devices do not transmit such higher frequencies to the same degree as they transmit the signal frequencies. Thus these higher frequencies will be suppressed or considerably attenuated when the signal reaches the receiving end of the system. Since the unexpanded signal received is different from that transmitted, when the received signal is expanded, the resulting signal is not a true representation of the original signal. In attempting to expand the signal received, higher frequency distortions are introduced. These frequencies in the case of sounds are very noticeable. When, however, the intensity of the signal wave is used as the controlling function, the above diiiiculty is eliminated. Such a controlling function when used to compress the signal will not introduce noticeable distortion. A signal so compressed is readily transmitted by the transmitting system, and at the receiving end the unexpanded signal is substantially identical with that transmitted. Thus when the signal is expanded, it will be a true reproduction of the original signall with no distortion due to compression and expansion.

Since a signal wave possesses, in addition to its intensity, various instantaneous amplitudes, the problem of obtaining a regulating quantity dependent only on the intensity of the signal Wave without the introduction of distortion is a particularly diflicult one. I have discovered, however, that if the signal be used to modulate a higher frequency carrier wave, a quantity varying directly as the intensity of the signal wave may be obtained. I obtain such a quantity at the transmitting end of a system, and use it to control the gain of an amplifier or to regulate an attenuator to effect compression of the signal to the desired range of intensities. At the receiving end I obtain a similar quantity in a like manner, and use it to control the gain of an amplier or to regulate an attenuator to effect expansion of the signal to its original range of intensities or any other range which may be desired.

In order to explain the manner in which I obtain this regulating quantity, the following discussion of certain principles of the theory of modulation is given. In the following discussion as well as in the rest of the application and claims, the term signal means variations of relatively low frequencies, such as, for example, audio frequencies or any other desired frequency, whether of audio frequency or not. lso the term carrier means variations of any frequency whatsoever which is considerably higher than the signal frequency.

An electrical signal voltage Vk corresponding to any signal usually consists of the sum of a plurality of sine wave components, and may be represented as follows:

where Ekzintensity of a component of signal voltage ,fkzfrequency of same component of signal voltage akzphase angle between said component and any reference sine wave Equation 1 The symbol 2k indicates a summation of Values due to each individual component of the signal, lc assuming various values one for each signal component. A carrier frequency voltage VC can be represented as follows:

VczEC cos @friet-H5) Equation 2 where Ec=intensity of the carrier voltage fczfrequency of the carrier voltage zphase angle between carrier voltage wave and the same reference sine wave in Equation l.

When the carrier voltage is modulated by the signal, the resulting current or voltage wave Vp will be a complex wave having the following form:

EEk i E 21r(f- 5,) f-lafg, Equation 3 Ck G The first term on the right-hand side of Equalli) tion 3 indicates that one component of the resulting wave is of a frequency equal to the carrier frequency. The second terni indicates a second component consisting of a group of Waves having frequencies of the surn of the carrier and the signal frequencies. The third term indicates a third component consisting of a group of waves of frequencies of 'the difference of the carrier and the signal frequencies. The second and third terrns are called the upper and lower side bands. Since the frequency of the carrier Wave is high in comparison with the signal frequencies, the frequencies of the side hands will be of the order of the frequency cf the carrier wave.

in accordance with iny invention, the carrier frequency component and one of the side hands are separated freni the wave represented hy Equation 3, leaving but one remaining side hand. Since Ec, the intensity of the carrier voltage is ordinarily substantially constant, it will 'ce seen that the intensity of the remaining side band depends solely on the sum of the individual intensities of the individual components of the Isignal voltage wave. This in accordance with my definition given above is the intensity of the signal. l rectify this remaining side band icy seine suitable rectifier, and therefore obtain a pulsating direct current, the intensity of the pulsations depending directly on some function the intensity of uhe signal. As pointed out aocve the frequency of these pulsations is of the ci u: of the carrier frequency, and therefore much higher than the signal frequei Due to large differences between these frequencies, the pulsating current can he smoothed out to elirnie the pulsaticn frequency without introduc ing any distorting factors either into the signal or into its intensity variations when the smoothed direct current is used to obtain regulating voltages for an amplifier or an attenuator. Such a smoothed current will have a value iR, which is a direct function of the intensity of the signal and can be expressed as follows:

where i) the function has a forni depending on the characteristics of the associated apparatus.

As a rnatter of fact it may not he necessary to smooth. out the pulsations, for example, in the transmission of sound, since their frequency is so high that any regulating factors which they introduce cannot be heard hy the listener, being considerably outside the audible range. When IR used to obtain a regulating voltage VF. for regulating the gain of arnpliner or to control an attenuator, voltage will liliewise be a direct function of the .intensity of the signal. Such a regulating quantity as pointed out above is an ideal one for use in the cornpression and expansion of a signal. By this arrangement i obtain a regulating quantity which I use to control the gain of amplifiers or to regulate an attenuator in opposite directions at the opposite ends of a transmission system.

A system which incorporates my invention is shown in Fig. l. This system is shown as one for transmitting signals from a transmitting to a. receiving end. At the transmitting end, signals coming from some suitable source l, such as a microphone or the like, are impressed upon an amplier or attenuator 2. The signals are also used to modulate carrier frequency currents coming from an oscillator e in a modulator 5. An amplifier 6 may be interposed between the Equation l source 1 and the modulator 5 in order to increase the signal strength to a value suitable for modulation. t is necessary to eliminate the carrier frequency from the wave resulting from the modulation of the carrier wave 'ny the signal. This may be done, for example, in the modulator 5 itself hy making it a balanced modulator as will he described below. Thus the output of the modulator 5 contains only the two side bands. This output is passed into a hand-pass filter 7, which blocks the passage of one of the side hands and allows the other side band to pass through substantially unaffected. The output of the hand filter 'l passed to a rectifier 8 which also nfay contain ineans for sinootlnng out the high frequency in the output of the rectifier. An amplifier rnay be interposed between the filter l and the rectier 8. The amplifiers 6 and ce can ce used not only to increase the strength of the signal which is impressed on it, but by selecting and/or regulating these ainpliners, the output characteristics of the rectifier 8 with reference to the signal con ing froml the source l may be made to assume any desired shape. It is also possible in rnany cases to omit the ampliers 6 and 5G and obtain t e desired output characteristic for the rect ier 3 hy properly selecting and adjusting 'the rectifier as well as the various other elements present in the system. Thus across the output t terminals of the rectifier 8 there appears a voltage which is a direct function f the intensity of the signal. 'ilns voltage is irnpressed the arnpliner or attenuator 2 in any suitable manner to control the gain thereof in the case of an amplifier or to control the attenuating power thereof in the oase of an attenuator. The voltage is arranged to effect a compression of the intensity range of the signal at the transmitting end of the sys-tern. The output of the amplifier or attenuator 2 is transmitted over any transmitting system, indicated by the dotted lines 3, which system can only transmit satisfactorily signals within a denite range of intensities. The cornpression effected by the regulating system is sufcient to keep the range of intensities of the transmitted signal within this range. At the receiving end of the system the signal is impressed upon an arrangement similar to that described at the transmitting end. This arrangement at the receiving end consists of amplifier or attenuator 2', amplifiers 6 and 5G', oscillator 4', modulator 5', band-pass filters 7', nd rectifier 8', corresponding to the inernhers 2, 6, 60, e, 5, 7 and 8 as described above. The output voltage of the rectifier 8', however, is impressed upon the amplifier or attenuator 2' to effec;l an expansion of the signal so as to bring it back to its original range of intensities or to any other desired range of intensities. The output of the amplifier or a+- tenuator 2 is passed to some suitable output device, such as a loud speaker i'.

In sorne instances it may not he necessary for the band-pass lter 'l to pass all of the frequencies of the side band to the degree. For eX ample, in the case of telephone lines, the higher frequencies of the signal cause relatively greater amounts of cross tallr in adjacent telephone lines than at the lower frequencies cf the signal. Thus the permissible upper limit of the intensities of 'the higher frequency components of the signal is less than the permissible upper limit of the intensity of the lower frequency components. By having the band-pass filter pass only the higher frequencies of the side band, the output of the rectifier 8 will have a value which is a function of the intensity of the higher frequency components of the signal. Thus the gain or attenuating power of the ainpliiier or attenuator 2 will be controlled directly as a function oi the intensity of said portion of the signal. This is exactly the result which is desirable in telephone lines as stated above. 1n other instances it may be desirable to pass only the lower frequency components of the side band, and regulate the gain or attenuating power of the amplifier or attenuator as a function of the intensity of the lower requency components of the signal. In other cases the iilter may pass the frequencies at one end of the side band substantially unaffected, and attenuate the components of signal increasingly as their frequencies approach the other end oi' the band. In any case, however, since the controlling factor is still a function of the intensity of a component of the signal, the compression and eX- pansion which the signal undergoes in my system is substantially as free from distortion as when the entire side band is passed.

The disclosure in Fig. l, although diagrammatic, shows the basic features of my invention and a wide variety of specic arrangements can be used for each of the elements indicated as will readily suggest themselves to those skilled in the art. However, in Fig. 2 1 show certain specific arrangements which can be employed. Since the receiving and transmitting ends of the system may be substantial duplicates, merely show the details of the transmitting end. Since the ampliers 6 and 60 may be any oi a wide variety of types and since the construction of such amplifiers is well known, they are not shown in detail in Fig. 2. Likewise since the construction of band iilters is well known and since any type can be utilized as the ilter 7, it is believed unnecessary to show a speciiic form of such a filter, Fig. 2 shows, however, a specic form of modulator which can be used for modulator 5. The output of the amplifier 6 is impressed on the primary winding 9 of a coupling transformer 10. The opposite ends of the secondary l1 of the transformer l0 are connected to the respective control grids 12 and 13 of the space discharge tubes 14 and l5. The cathodes 16 and 17 of the tubes le and l5 connected by means of a common connection to the mid-point of the secondary 1].. A biasing source oi potential, such as a battery 18, may be interposed in this connection. Also in this connection is a secondary coil 19 inductively coupled to a primary coil 26 upon which is impressed the output oi the oscillator ll. The two anodes 2l and 22 of the tubes 14 and 15 are connected to the opposite ends of the primary 23 of an output transformer 24. The midpoint of the primary 23 is connected through a source of anode potential, such as, for example, a battery 25 to the cathodes. In order to enable the circuit and tube parameters of the upper and lower halves of the circuit to be balanced, adjustable condensers 36, 36 are connected across each half of the secondary 1l. An output secondary 26 is directly coupled to the primary 23. This secondary 26 is connected to the input side of band-pass iilter 7. The signal voltage applied to the primary 9 will in the above arrangement modulate the carrier frequency voltage supplied to the primary 20. Ii, however, by adjusting the condensers 36, 36, all the circuit and tube parameters are balanced in the symmetrical upper and lower halves of the circuit, the carrier frequency will be balanced out in the transformer 24 and will not appear in the secondary 26'. Thus only the side bands will be' in the output of the modulator. The same result could of course be accomplished by using any other kind of modulator which does not balance out the carrier frequency, and utilizing a separate device for blocking out the carrier frequency and allowing the side bands to pass through it. Thus, for example, the device 7 could be arranged to block the passage of the carrier frequency as well as the frequencies or" one of the side bands.

The rectifier 8 may consist of the usual two electrode tube having a thermionic cathode 27 and an anode 28. One output terminal of the ampliiier 2!) is connected to the anode 28. The other output terminal oi" the amplifier 69 is connected through a resistance 29 to the cathode 27. A rectied current will 'low through the resistance 29 when alternating voltage from the amplifier 60 is impressed upon the rectier. In order to eliminate the high frequency pulsations o1" this direct current, a high frequency current bypass condenser 3l may be connected across the resistance 29. The desired regulating voltage will appear across the resistance 29, due to the iiow oi the output current of the rectifier through it. Since it may be desirable to utilize but a part oi' this voltage, the resistance 29 may be provided with an adjustable tap 32. The voltage between one terminal of the resistance 29 and the tap 32 is connected by means of conductors 33 and 34 to the amplier 2 for the desired regulating purposes. The reccculd, oi course, be of any other kind, such for example, the well-known grid detector tube in which a tube having a cathode, plate, and at least one control grid is used. In such a rectifier, the side band is impressed upon the control grid through a condenser bridged by a high resistance leak. As pointed out above, the output of the rectier could be used to obtain a regulating voltage even without any smoothing device for said output.

The device 2 upon which the output of the rectier exerts its regulating eiiect may consist of a plurality of amplifierstages 6l, 62 and 63. One or these stages, for example, 63, shows in detail one form of an amplifier stage which may be used. This stage consists of a space discharge tube 64 of the pentode type. This tube has an indirectly heated thermionic cathode 65, an anode 56, control grid 67, a screen grid 68, and an auxiliary grid 69. The input to this amplier is impressed between the thermionic cathode 65 and the control grid 57. A coupling condenser 70 may be interposed in the connection to the control grid. The anode 66 is connected through a resistance Z1 and a source or" potential 72, such as, for example, a battery to the thermionic cathode 65, in the usual manner so that the anode 66 is maintained at a positive potential wit respect to the cathode. The screen grid 68 is connected in the usual manner to a point in the source of potential 72 less positive with respect to the cathode than is the anode 66. The auxiliary grid 69 is connected directly to the cathode. The output from the anode 66 passes through the resistance 71 back to the cathode 65. Thus an output potential will appear across the ends of the resistance 7l. Any portion of this output may be taken oil by means of an adjustable contact 75 on the resistance 7l, said contact going to one output terminal, the other output terminal being connected to the cathode 65. The regulating potential which appears in the output of the rectifier 8 is impressed between the cathode 65 and the control grid 67, by having the conductor 34 connected directly to the cathode and the conductor 33 connected to the control grid 67. Interposed in this latter connection may be a high resistance '76. In order that the tube 64 may be enabled to operate on the desired portion of its characteristic, a source or biasing potential, such as a battery 27, is also interposed in said latter connection, whereby the proper bias is impressed upon the control grid 67. If the conductors 33 and 34 are so connected that the control grid 67 becomes increasingly negative with an increase in the output or" said rectifier, the amplifying power or the gain of the tube 64 will decrease with an increase in said rectiner output. Under these conditions, the amplifier stage 63 will effect a compression of the signal impressed upon it. The output voltage from the rectiner 8 is also shown as being impressed upon each of the stages 6l and 62. rIhe arrangement with respect to each of these stages may be similar to that shown in stage S3. -Iowever, seine instances it may not be necessary to impress the regulating eiect on all of the amplifier stages, in which cases the compression efected by those stages upon which the regulating voltage is impressed is suicient for the particular system in which the arrangement is used. `Also it is not necessary to use the particular number of amplifier stages shown, inasmuch as a fewer or a larger number may be satisfactory in various arrangements. Of course it will be understood that at the receiving end of the system, in order to effect an expansion of the signal, it is merely necessary to impress the output of the rectifier 8', corresponding to the rectifier 8, upon the ampliel' in such a manner that the bias on the control grid 67 becomes deoreasingly negative with an increase in the output of said rectiiier. Where a system such as l have shown in Fig. 2 is to oe used sometimes as a sending and sometimes as a receiving device, it is merely necessary to provide switching means to connect either the source l or the receiving end of a transmission line tc the input or the device, and to reverse the connection of the leads 33 and 34 to the ampliiier 2 in order to reverse the polarity of the biasing voltage supplied rorn rectiiier 8.

When the signal intensity supplied to such an arrangement as I have described above is plotted in decibels above and below a reference level against tde output intensity, we obtain the characteristic curve of the device. Fig. 6 represents a set of possible characteristic curves for an embodiment of rny system. ln this figure c represents the characteristic curve of the compressor of my system, b the characteristic curve for the expander, c the combined characteristic curve oi niy combined system. Let us suppose that a transmission line can handle a range of signal intensities in decibels half as large as that o the original signal. If: the range of input intensities lies between the points m and n, then the corresponding output of the compressor' as deter -iined by the curve d will lie between the distance o, p for the system half ci the distance m, o. This is a relationship w ich shown in Fig. 6. In expanding, a signal lying between points q and r, which .r ge is equal to the range between o and p, i .pressed on the expander ch produces an output a range of intensities lying between the points t and u as deternined by the curve c. ln order that the ander signal be exactly equal to the original y m, n. This is relationship which is shown in Fig. 6. Since curve b is the resultant of curves a and c, the end point c will be determined by the points u and 1t, and the other end point w will be determined by the points m and t. In order that the entire range of intensities be reproduced exactly, the curve b should be a straight line between the points c and w. However, this requirement does not exist with respect to the curves a c. It is immaterial what particular s' "le the curves c and c assume as long as the resc" ant curve b is a straight line, as stated above, these curves a and c being shown as straight lines in Fig. 6. ln sonic instances it may be desirable that curve b be linear only up to a certain point, such as, for example, in the case of very loud which the ear does not disstraight lines in Fig. 6, it is somewhat dinlcult to obtain such characteristics in actual practice. The char Icteristic curves as shown in Fig. 'l are a closer approximation to those characteristics ci the arrangements which I prefer to use. shows curves c, b and c similar to those Fig. 6. Curves c and c in Fig. 7 are or" Xponential forro, and bear such a relationto each other that the resultant curve b is still a straight line. t will be noted upon inspection of curve c that the maximum range of signal intensities m, n which will be impressed upon the compressor will give an output range of signal intensities o, p to be transmitted over the transmitting syst-ern, which has the requisite value of half of m, n. The expansion effected by the expander having the characteristic c will, as stated above, give an output signal whose range ci intensities t, u is exactly the same as the original signal.

Since in most instances it is desirable to provide expander a compressor whose characteristics bear definite 4relationships to each other, as pointed out above, it is desirable that sonic control of these characteristics may be had. r'rhis may be accomplished by the proper selection, regulation and combination of various ectifiers and ampliiiers.

The manner in which such control be had will be better understood by referring to some of the characteristic curves of the various elencents involved.

Fig. 8 shows the automatic gain requirements or a system to obtain the forni of characteristics shown in Figs. 6 and 7. En this figure the input voltage from an input device, such as the source l, is plotted against the gain of the amplifier 2 in decibels. The gain in decibels can be expressed as follows:

V2 Gain 1n Db=20 log /-I Equation 5. in which V2 represents the output voltage of the system, "J1, the input voltage thereto.

n figure, curve a represents the requirement to obtain the characteristic as shown in Fig. 6, and curve b represents the requirement to obtain the characteristic shown in Fig. '7.

9 is a curve showing the general relationbetween the voltage input to the ainplier 6 and the automatic biasing voltage appearing across the resistance 29 in the output of the rectiiier 8 in one particular instance of such an arr .ngel/nent. Of course it will be understood 'that the actual curve obtained will vary in each case, and the shape of the curve can be changed by using different types of amplifiers and rectiers in the system between the device 1 and the outputY of the rectier 8.

Fig. shows the required gain curve for an amplier fed fromV an automatic biasing device having thecharacteristic shown in Fig. 9 to obtain the characteristic b of Fig. 8. In Fig. 10 the automatic biasing voltage is plotted against the gain in decibels of the amplifier.

Having Vobtained the required form of curve as shown in Fig. 10, it is necessary now to refer to the actual characteristic curves of various Y'amplifiers.

Fig. 1l represents typical curves obtained from various types of Vamplilers. Curve a represents the characteristic of an amplier stage, such as 63 shown in Fig. 2, the total bias applied to the control grid 67 being plotted against the gain in decibelsgof said ampliner stage. It will be noted that although portions of said curve may Vapproximate the required curve, as shown in Fig. 9, yetY it may be necessary to obtain some modiiication' of the characteristic curve of the entire amplifier Y tube in order to obtaina more faithful approximation to the requiredcharacteristic. VIt will be understood that the portion of the characteristic of the amplier stage 63, as utilized in the device, can be regulated by regulating the value of the xed biasing potential 77.

When the automatic biasing voltage instead of being applied to the control grid is applied to the screen grid, an entirely different characteristic is obtained. Curve b in Fig. l1 shows such a characteristic while Fig. 3 illustrates a specific embodimentrof an arrangement in which the Yautomatic biasing voltage is so'applied. In Fig. 3 the same reference numerala are applied to those elements which are identicalV with those in Fig, 2. It will be noted that the arrangement in Fig. 3 is exactly the same as that shown for the amplifier stage 63 shown in Fig. 2, except that the automatic biasing voltage appearing between the leads 33 and 34 are impressed between the cathode 65 and the negative end of the biasing battery 72. Such an arrangement adds the automatic biasing voltage directly to the screen grid voltage, and results in Va characteristic curve for the arrangement, such as b in Fig. 11. For this curve the total bias applied to the screen grid 68 is plotted against the gain in decibels of said amplifier stage. The particular numbers appearing on Fig. Il are merely inserted as an example oftypical values, for the purpose of showing the relationship between curves a, and b, and are not to be construed in any limiting sense.Y The particular portionfof the characteristic curve b, which is utilized, can be regulated by regulating the value of the biasingrpotential applied to the screen electrode by the source 72. From curve b it will be seen that if the automatic biasing potential across conductors 33 and 34 is so applied that the screen grid becomes decreasingly positive with an increase in signal intensity, a compression of the intensity range of the signal will result, while if the automatic bias-voltage is applied in the opposite direction, an expansion of the intensity range will be obtained. By combining diiierent portions of curves a and b, an infinite varety of resulting characteristics can be obtained, one of which will closely approximate the curve as shown in Fig. 1G. @uch a combination can be made, for example, by using the arrangement shown in Fig. 3 as one of the stages 61 or 62. Of course the particular order of the amplifier stages can be changed, that is, the amplier stage shown particularly as 63 Yin Fig. 2 can be utilized as any one oi the amplifier stages 6l, 62 or 63, while the arrangement as shown in Fig. 3 can be utilized as any one of the remaining amplifier' stages.

Instead of combining the characteristics a and b in two- Yseparate stages, it is possible for such a combination to be made in a single stage using but a single pentode tube. Fig. 4 is an example of such an arrangement. In this gure likewise the same reference numeralsrare applied to those elements which are identical withY those in Fig. 2. In Fig. l a resistance 78 is connected between the positive terminal of the biasing battery 77 and the negative terminal of the battery 72. An adjustable Contact 79 connects the cathode 65 to a point intermediate the ends of the resistance 78. The automatic biasing voltage appearing between the conductors BS'and 34 is applied across the endsr of theresistance 78. Thus a portion oiV the automaticb-iasing voltage will be impressed upon the screen grid 64, while the remaining portion thereof will be impressed upon the control grid V67. By adjusting the contact 79 along the resistance 78, the proportions of the automatic biasing voltage which are applied to the two grids can be varied in anyV desired manner. Thus any desired portions of the curves a and'i'b can be combined to obtain any desired characteristic.Y Of course in each case a control of the'portion of the characteristic operated upon can further be obtained by regulating the biasing potential 77 or the position of the screen grid lead along the source 72.

Although I have described amplifiers using speciiically appentode tube, yet anir other kind of amplifier tube can be used. For example, a screen gridtube could be used in which the auto-- matic biasing potential would be applied either to the control grid, the screen grid, or to both. These arrangements could be represented by the showing in Figs. 2, 3 and ll, merely by the omission of the auxiliary grid 69 in eachV case. Also a triode tube could be utilized, in which case the automatic biasing voltage would be applied to the control grid. Each of such arrangements would,

of course, give av diierent characteristic curve.

Furthermore, any combination of any of these arrangements could be utilized by using any oi such arrangements in any of the stages 51, 62 or 63, while if necessary more lstages, could be added using still otherarrangements to obtain a desired characteristic.

As stated above, it is not necessary that the elements represented by 2 or 2' in Fig. 1 be such ampliers as shown in Figs. 2, 3 and 4, or as described above. For'example, such an arrangement as that shown in Fig. 5 could be used. In this arrangement, the output of the source of signals 1 is passed through an attenuating device 80. This attenuating device may consist, for example, of a non-inductive resistance potentiometer 81. It will be seen that the signal passing from the source 1 through potentiometer 81 will be attenuated in value. In order to control the degree to which the signal is so attenuated, the potentiometer 81 may be provided with a movable contact arm 82 which regulates the portion of the input voltage which appears across the output terminals. The contact arm may bermoved along the potentiometer 8l, for example by a suitable galvano-meter arrangement 83. This galvanometer is fed from the conductors 33 and 34. Thus the contact arm 82 will be moved in accordance with the value of the output of the rectiiier 8. The degree to which the signal coming from the source 1 is attenuated will likewise be regulated by the output of said rectifier 8. In this arrangement it may not oe necessary to rectily the output of lter 7 inasmuch as tne galvanorneter may be or tlie A. C. type. Ol course other devices which control tl'le signal directly in response te an A. C. voltage may be used without t'ne rectifier. l tlie galvanoineter arrangement 33 is so constructed tnat the oo' .ct 82 selects a smaller portieri or the input voltage to be supplied to t`ne output terminals as the intensity o tne signal increases, then the si e will be compressed in its intensity range, W e il tne Contact arm inoves in tlie opposite direction with an increase in signal intensity, the signal Will oe expanded in itsx intensity range. It may be desirable to interpose ampliiiers Se and 85 before and after the attenuating device Si) in order that the signal strengt'n may be kept up to the proper value. Of course any other arrangement ivi cli attenuates the signal and Whose attenuatingl power can be controlled could ee used instead oi? the potentiometer 8l.

The invention is not limited to t -e particular details of construction described aiiove as many equivalents will suggest themselves to tnose skilled in the art. it is accordingly that the appended be given a broad interpretation commensurate with the scope of tne invention Within the art.

What is claimed is:

l. A signal control systein eoinnrisi-fig a source oi signal producing Vsignals consi or" the oi one or incre perle-tical.u -varying components, each having a certain peak intensity, the summation ci said peak intensities con- .ting tlie intensity oi signal, the signals roduced having a varying intensi' a device i tne srengti of s .als and ineens autoin- .ccally responsive to the iisity oi said signal for varying the degree to which changes tire strength oi said signals in Jccordance i li said signal intensity.

2. A signal control system comprising a source oi signes producing signals consisting of the summation of one or ino-re periodically-varying components, eael'i having a certain intensity, t'ne sunarflatif oi said i tensitles con-- stituting the identity of signal, tile signals so produced l 'ntensity, an arnliier for ainplnying and means utornatically responsive to tile intensity of said 'e al for vary' tne of anipliers in 3. A signal control system comprising a source of producing signals consisting of the sunnnation oi' one er more periodically-varying components, caen lia-ving a cert peel: intend peak in ,n cond signal, the signals .ensity, at-

' nale, and means intensity or said stitnt so produced liaving a vatenuator tor 'utoniatically responsive to tb signal for varying the attenuat ig power or said attenuator in accordance with said signal intensity.

ties of the signals Corning frein said source', said means conflprisin'.y a device for changing the strength of said signals, and means automatically -esponsive to ne intensity of said signal for varytlie degree to which said device changes the strength ci said signals in accordance with said signal in'.ensity.

5. A signa1 control system comprising a source of signals noducing signals consisting of the summation oi one or more periodically-Varying components, eac'n a. certain pea-lr intensity, the summation. of pealr intensities constituting the intensity ci said signal, the signals so produced naving a varying intensity, a signal transmission device which can transmit satisfactorily signals having a range of intensities less than tiie of ine signals produced by said source, arrangement at the transmitting end ci said device including means to compress the range oL intensities of the signals coming from said source, said means comprising a device for changing the strength of said signals, and means automatically responsi e to the intensity or" said signal for varying tlie degree to which said device cnarees the strength of said signals in accordance wsaid signal intensity, and an arrangement at the receiving end of said device including rneans to expand the range of intensities of the signals received, said means automatically comprising a device for changing the strength of signals, and means responsive to the intensity or tlie signals received for varying the to which device changes the strength received signals in accordance Witli tlie intensity of said received signals.

e. l con foi syst/ein comprising a source signals ,having a varying insign-als, a source or current for a carrier frequency with. respect to said signals, means for modulating said carrier current by said signals, means for separating from the modulated carrier wave currents of frequencies lying Wholly Within one sand, and means responsive to tlie intensity or said separated currents for varying the degree to which said device changes tile strength of said signals in accordance Wit said separated currer t intensity.

7. A signal control system comprising a source of signals producing signals having a varying intensity, a device for changing lie strength oi signals, a source or current of a car.. frequency with respect to said for modulating carrier current by signals, ineans for separating one side band the modulated ng a sou 1ce a varying inng said signals, ireduency with ier modulating d signal ineens for tne modulated carof signals produc... e tenf'it", an ainpliier a source or" c means for obta ring a lating voltage in accordance ivitl'i tlie die o rectified side band, ineens i impressing regulating voltage on sad amplifier to the gain rier current, means for rectifving side band,

yan

of said amplier in accordance with said magnitude.

9. A signal control system comprising a source of signals producing signals having a varying intensity, an attenuator for attenuating said signals, a source of current or a carrier frequency with respect to said signals, means for modulating said carrier current by said signals, means for separating one side band from the modulated carrier current, means ior rectiiying said side band, means for obtaining a regulating voltage in accordance wit the magnitude of said rectified side band, and means for impressing said voltage on said attenuator to regulate the attenuating power of said attenuator in accordance with said magnitude.

10. A signal control system comprising a source of signals producing signals having a varying intensity, a device for changing the strength of said signals, a source of current of a carrier frequency with respect to said signals, means for modulating said carrier current by said signals, means for separating from the modulated carrier wave currents of frequencies lying wholly within one side band, means for rectifying said separated currents, means for obtaining a regulating voltage in accordance with the magnitude of said recthied currents, and means ior impressing said voltage on said device to vary the degree .to which said device changes the strength of said signals in accordance with said magnitude.

11. A signal control system comprising a source of signals producing signals having a varying intensity, an amplier for amplifying said signals, said ampliiier including a space discharge tube having a cathode, an anode, and at least one control electrode, upon which control electrode the signal to be ampiiiied is impressed, a source of current of a carrier frequency with respect to said signals, means for modulating said carrier current by said signals, means for separating from the modulated carrier wave currents of frequencies lying wholly wit-hin one side band, means for rectirying said separated currents, means for obtaining a regulating voltage in accordance with the magnitude of said rectified currents, and means for impressing said regulating voltage on said control electrode to vary the gain of said arnpliiier in accordance with said magnitude.

l2. A signal control system comprising a source of signals producing signals having a Varying intensity, an ampliiier for amplifying said signals, said amplifier including a space discharge tube having a cathode, an anode, a screen electrode for said anode, and at least one control electrode, upon which control electrode the signal to be amplified is impressed, a source of current of a carrier frequency with respect to said signals, means for modulating said carrier current by said signals, means for separating from the modulated carrier wave currents or" frequencies lying wholly within one side band, means for rectiiying said separated currents, means for obtaining a regulating voltage in accordance with the magnitude of said rectied currents, and means for impressing said regulating voltage on said screen electrode to vary the gain of said ampliiier in accordance ith said magnitude.

13. A signal control system comprising a source of signals producing signals having a Varying intensity, an amplier for amplifying said signals, said ampliiier including a space discharge tube having a cathode, an anode, a screen electrode for said anode, and at least one control electrode, upon which control electrode the signal to be ampliiied is impressed, a source of current of a carrier frequency with respect to said signals, means for modulating said carrier current by said signals, means for separating from the modulated carrier wave currents oi frequencies lying wholly within one side band, means for rectifying said separated currents, means for obtaining a regulating voltage in accordance with the magnitude of said rectified currents, means for connecting said regulating voltage between said control grid and said screen grid, an impedance connected to said last-named means across said regulating voltage, said cathode being connected to a point intermediate the ends of said impedance.

ill. A signal control system comprising a source of signals producing signals having a varying intensity, an amplifier for amplifying said signals, said amplier including a space discharge tube having a cathode, an anode, a screen electrode for said anode, and at least one control electrode, upon which control electrode the signal to be amplified is impressed, a source of current of a carrier frequency with respect toi said signals, means for modulating said carrier current by said signals, means for separating from the modulated carrier Wave currents of frequencies lying wholly within one side band, means for rectiiying said separated currents, means for obtaining a regulating voltage in accordance with the magnitude of said rectied currents, means for connecting said regulating voltage between said control grid and said screen grid, and an impedance connected to said last-named means across regtdating voltage, said cathode being adjustably connected to a point intermediate the ends of said impedance.

i5. A amplifier comprising a space discharge tube including a cathode, an anode, a screen electrode for said anode, and at least one control electrcde upon which control electrode the signal to amplified is adapted to be impressed, an electrical circuit connecting said screen electrode and said control electrode, an impedance in said circuit, said cathode being connected to a point intermediate the ends or" said impedance, means for obtaining a regulating voltage varying in accordance with a regulating quantity, means for connecting said regulating voltage across said impedance, and an output circuit connected to said amplifier.

16. An amplier comprising a space discharge tube including a cathode, an anode, a screen electrode for said anode, and at least one control electrode upon which control electrode the signal to be amplified is adapted to be impressed, an electrical circuit connecting said screen electrode and said control electrode, an impedance in said circuit, said cathode being adjustably connected to a point intermediate the ends oi said impedance, means for obtaining a regulating voltage varying in accordance with a regulating quantity, means for connecting said regulating voltage across said impedance, an output circuit connected to said ampliiier.

17. An amplier comprisin0r a plurality of arnpliiier stages, one of said stages including a space discharge tube including a cathode and at least one control electrode, another of said stages including a space discharge tube including a cathode, an anode, a screen electrode for said anode, and at least one control electrode, means for iinpressing the input to each or said stages upon the respective control grid, means for obtaining a :regulating Voltage varying in accordance with a regulating quantity, means for impressing said regulating voltage upon the control electrode of said rst-named stage to control the gain of said stage in accordance with said regulating voltage, and means for impressing said regulating voltage upon the screen electrode of said secondnamed stage to control the gain of said stage in accordance With said regulating voltage.

18. A signal control system comprising a source of signals producing signals consisting of the suinmation of one or more periodically-varying components, each having a certain peak intensity, the summation of said peak intensities constituting the intensity of said signal, the signals so produced having a Varying intensity, a signal transmission device Which can transmit satisfactorily signals having a range of intensities less than 'the range of signals produced by said source,

means to compress the range of intensities oi the signals coming from said source, said means cornn prising a resistance potentiometer interposed be tween said source and said transmission device for attenuating said signals, and means automatically responsive to the intensity of said signals for varying the portion of the signal Voltage applied to said potentiometer which is impressed on said transmission device to vary the range of intensity of said signal.

19. The method of varying the intensity range of a signal which comprises modulating a carrier frequency Wave with said signal, separating from the modulated carrier Wave currents lying Wholly within the frequencies of one of t'ne resulting side bands, rectifying said separated currents, and regulating the strength of the signal in accordance with the magnitude of said rectified current.

20. The method of varying the intensity range of a signal which comprises modulating a carrier frequency Wave with said signal, separating from the modulated carrier Wave currents lying Wholly within the frequencies of one of the resulting side bands, and regulating the strength of the signal in accordance with the intensity of said separated currents.

21. The method of obtaining a regulating quantity in accordance with the intensity of a signal which comprises modulating a carrier frequency wave with said signal, separating from the modulated carrier Wave currents lying Wholly Within the frequencies of one of the resulting side bands, and using said separated currents to obtain a regulating voltage in accordance With 'the intensity of said separated currents.

HAROLD BEIZER. 

